280 



THE DIGESTIVE ORGANS. 



lymph-cells. It should be remembered that every nodule may 

 possess a germ center. Peyer's patches are collections of these 

 lymph-follicles. The surface of the nodule presenting toward 

 the lumen of the intestine is covered with a continuous layer of 

 intestinal epithelium. In man the summit of that portion of the 



^ Intestinal epithelium. 



Lumen of gland. 



Goblet cell. 



Mucosa. 



Mucosa. 



Muscularis mucosae. 



Fig. 220. From colon of man, showing glands of Lieberkiihn ; X 2O - 



nodule projecting into the lumen of the intestine presents but a 

 slight depression of the intestinal epithelium, while in some animals 

 (guinea - pigs), and especially in the nodules composing Peyer's 

 patches, there is a deeper depression, even leading to the formation 

 of a so-called "crypt" or "lacuna" (vid. Fig. 219). At the 

 summit, the intestinal epithelium where it cornes in contact with 

 the lymph-nodule, is peculiarly altered. In most cases there is 

 an absence of a basement membrane, the epithelium resting 

 directly upon the lymphoid tissue. No clearly defined boundary 

 between the two is distinguishable (intermediate zone of v. David- 

 off) ; they are therefore in the closest relationship to each other. 

 The basal surfaces of the epithelial cells are fibrillar, the fibrils 

 seeming to penetrate into the adenoid reticulum of the follicles. 



